Is it permissible to use hashish once a week to relieve headaches and dizziness associated with its withdrawal, knowing that one is regular in prayer?

Using hashish is a major sin (kabirah), and it is more vile than alcohol. One must completely abstain from its use. Every warning (wa'id) that applies to theen wine-drinker also applies to the hashish user. It is not permissible to consume it, neither for medicinal purposes nor for any other reason, for Allah has not placed cure in that which He has forbidden.